| Spodoptera picta(S.picta)and Spodoptera litura(S.litura)are the closest species among the spodoptera genus,the species separation of those two insects is occurred only about 3 million years ago.They have many similarities in many aspects such as the geographical distribution,life cycle,morphological and behavior characteristics.However,they have completely different feeding habits.S.litura is extremely polyphagy and glutonly in the larval stages that is harmful to hundreds of economic crops seriously.On the contrary,the host plant of S.picta is limited to the amaryllidaceae,and Crinum asiaticum(C.asiaticum)is the most common choice for them.Lycorine is the main alkaloid of C.asiaticum,which is abundant in the different parts of the plants.The secondary substances of plants,which are toxic to insects,are considered as the defense system to against their pests.When insects eat the plants containing the secondary substances,their detoxification system will be activated such as cytochrome P450 enzyme family(cytochromeP450,P450s),carboxylesterase family(carboxylesterase,CarE),glutathione-S-transferases(glutathione-S-transferases,GSTs)and other detoxification genes to detoxify the secondary substances.Thus insects co uld adapt to host plants.To explore how host plants effect the development of insects,we use S.litura and S.picta for rearing experiments by exchanging the host plant of two species.Then we feeded C.asiaticum and artificial diet that mixed with lycorine and the analyzed how lycorine was metabolized or detoxified in those two insects that we detected the metabolites of lycorine in different tissues and excrements by GC-MS.We annotated detoxified related gene family APNs,COEs and GSTs of S.picta.Finally,we screened and compared the genes from APNs,COEs and GSTs that highly induced by lycorine in S.litura and S.picta by RNA-seq.The main results are as follows:1.Analysis of adaptability of S.picta and S.litura to C.asiaticum plantsWe use C.asiaticum leaves,which the host plant of S.picta to feed the larvae of S.litura from the first instar found that all the larvae of S.litura were dead in the before forth instar.When we use the S.litura’s host plants Chinese cabbage,tobacco,m ulberry leaf,sweet potato leaf,soybean and carrot to feed the larvae of S.picta,we found that s.picta can eat all of those plants,however only the larvae that eat artificial diet,mulberry leaves and soybean could survive though the development was delayed;others which ate cabbages,tobacco or potato leaves were all dead in the larval stage.In order to keep the strain of S.litura that can eat C.asiaticum,we mixed the grinded crinum leaves with artificial diet to feed the larvae;the development of the S.litura was delayed at the first and second generation,the development of S.litura became the same as control that means the S.litura was adapting to the low content of C.asiaticum.Noteworthy,with we found five larvae of S.litura,which have abnormal color pattern in the third generation.The body color of the larvae changed from dark brown to light green,the body color of the young pupa changed from light yellow to light green,the scales on the abdomen and back of the ad ult changed from dark red to light yellow and tended to the scales on the abdomen of S.picta,while S.picta had no change when it was fed to the third generation compared with the control group.The res μLts showed that S.picta could feed on and metabolize C.asiaticum,and S.litura had an important effect on the morphological development the feeding of Crinum asiaticum.2.Analysis of the components of C.asiaticum and the response of lycorine to the diet of S.picta and S.lituraThe leaves of C.asiaticum were identified by GC-MS,the results showed that the higher alkaloid in C.asiaticum was lycorine.The results of qualitative analysis of standard products of lycorine showed that lycorine could be converted into Lycorine,1-0-acetyl-2-0-methyl-after derivatization.Separately add different concentrations of lycorine to the artificial diet and feed the 4th instar larvae of Spodoptera litura to deter mine the LD50 of lycorine is 0.81 mg/head.The artificial diet containing lycorine was used to lure the larvae of S.picta and S.litura respectively.The results showed that lycorine could attract the larvae of S.picta,but had no effect on the larvae of S.litura.3.Metabonomics analysis of S.picta and S.litura after feeding artificial diet containing lycorineThe larvae of L6D1 S.litura were fed with artificial diet containing 10 mg/g lycorine for 24 hours.Their excrements,epidermis,fat body,midgut,Malpighian tube and haemolymph were collected and identified by GC-MS.The results showed that lycorine and 1-o-acetyl-2-o-methoxy were found in the excrements supernatant mass spectrometry of S.picta and S.litura.At the same time,we found that there was a specific lycorine alkaloid anhydrolycorine in the faeces of S.litura,and there was no significant difference in the other components.Anhydrolycorine is an isoquinoline alkaloid containing ether and benzene ring.Because ether does not react with alkali,oxidant and reductant,nor with sodium metal,its performance is stable.We speculate that anhydrolycorine is not easy to combine with detoxification enzymes or some compounds in insects,so it is easy to accumulate in the body and produce toxicity,causing damage to the body,thus affecting the growth and development of Spodoptera litura.4.Comparative analysis of APNs,COEs and GSTs in S.picta and S.lituraWe annotated 18 APNs,89 COEs and 39 GSTs genes in S.picta.Compared to the S.litura,they phylogenetic tree analysis showed that the three gene families were quite conserve in those two species that most of genes were one to one in both insects.After 24 hours and 72 hours of feeding artificial diet containing 1 mg/g lycorine and artificial diet without any treatment,the midgut,fat body and malpighian tube of the larvae were collected and analyzed for transcriptome differential expression.It is speculated that in the long-term evolution process,S.picta has formed a unique system that can successfully metabolize lycorine,while S.litura does not have such a system,so although it still has the function of detoxification gene,it can not metabolize lycorine completely. |
PDF Full Text Request